[PATCH] mm: init_mm without ptlock

First step in pushing down the page_table_lock.  init_mm.page_table_lock has
been used throughout the architectures (usually for ioremap): not to serialize
kernel address space allocation (that's usually vmlist_lock), but because
pud_alloc,pmd_alloc,pte_alloc_kernel expect caller holds it.

Reverse that: don't lock or unlock init_mm.page_table_lock in any of the
architectures; instead rely on pud_alloc,pmd_alloc,pte_alloc_kernel to take
and drop it when allocating a new one, to check lest a racing task already
did.  Similarly no page_table_lock in vmalloc's map_vm_area.

Some temporary ugliness in __pud_alloc and __pmd_alloc: since they also handle
user mms, which are converted only by a later patch, for now they have to lock
differently according to whether or not it's init_mm.

If sources get muddled, there's a danger that an arch source taking
init_mm.page_table_lock will be mixed with common source also taking it (or
neither take it).  So break the rules and make another change, which should
break the build for such a mismatch: remove the redundant mm arg from
pte_alloc_kernel (ppc64 scrapped its distinct ioremap_mm in 2.6.13).

Exceptions: arm26 used pte_alloc_kernel on user mm, now pte_alloc_map; ia64
used pte_alloc_map on init_mm, now pte_alloc_kernel; parisc had bad args to
pmd_alloc and pte_alloc_kernel in unused USE_HPPA_IOREMAP code; ppc64
map_io_page forgot to unlock on failure; ppc mmu_mapin_ram and ppc64 im_free
took page_table_lock for no good reason.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 2 insertions, 2 deletions

diff --git a/arch/m68k/mm/kmap.c b/arch/m68k/mm/kmap.c
index 5dcb3fa35ea..fe2383e36b0 100644
--- a/arch/m68k/mm/kmap.c
+++ b/arch/m68k/mm/kmap.c
@@ -201,7 +201,7 @@ void *__ioremap(unsigned long physaddr, unsigned long size, int cacheflag)
                         virtaddr += PTRTREESIZE;
                         size -= PTRTREESIZE;
                 } else {
-                        pte_dir = pte_alloc_kernel(&init_mm, pmd_dir, virtaddr);
+                        pte_dir = pte_alloc_kernel(pmd_dir, virtaddr);
                         if (!pte_dir) {
                                 printk("ioremap: no mem for pte_dir\n");
                                 return NULL;
diff --git a/arch/m68k/sun3x/dvma.c b/arch/m68k/sun3x/dvma.c
index 32e55adfeb8..117481e8630 100644
--- a/arch/m68k/sun3x/dvma.c
+++ b/arch/m68k/sun3x/dvma.c
@@ -116,7 +116,7 @@ inline int dvma_map_cpu(unsigned long kaddr,
                         pte_t *pte;
                         unsigned long end3;
 
-                        if((pte = pte_alloc_kernel(&init_mm, pmd, vaddr)) == NULL) {
+                        if((pte = pte_alloc_kernel(pmd, vaddr)) == NULL) {
                                 ret = -ENOMEM;
                                 goto out;
                         }